Utilization of Fly Ash as Soil Amendments in Agricultural Fields of North-Eastern Gangetic Plains of India: Potential Benefits and Risks Assessments

Abstract

In recent decades, recycling or safedisposal of solid industrial wastes has become a prime environmental concernthroughout the world; and, fly ash (FA) is major amongst them. As a coalcombustion residue (CCR), FA is generated in large amounts by the thermal powerplants. In Indiaalone, more than 112 million tons of FA is generated annually, and theproduction is projected to exceed 170 million tons per year, by the year 2015.Normally, the bulk of the FA was dumped in landfills of open lands by dry andwet methods; but stringent environmental regulations are continuously enhancingthe cost of these types of disposal. Hence, many potential applications havebeen identified for the utilization and management of FA such as its use in cement, concrete, bricks, wood substitute products, soilstabilization, road base/embankments and consoli-dation of ground, landreclamation, and as soil amendments in agricultural fields.                 We used FA as soil amendment in agricultural fieldsand assessed its impact on soil health, and growth, physiological, biochemicaland yield responses of two major Indian crops, rice and mung bean, undernatural conditions. We used five different doses of FA amendments (FAA) – 0, 5,10, 15 and 20 percent. The soil, up to the depth of 30 cm, in each of the 1 m2experimental plots (in triplicate)  wasplowed up, and mixed homogeneously with FA (w/w ratio) of respective doses; andleft as such for fifteen days. After fifteen days, recommended doses of NPKfertilizers were applied for respective crops, and the seeds were sownfollowing conventional agronomical practices.                 Soilanalyses revealed that FAA had improved the physico-chemical and mineralogicalproperties. Soil nutrients like Na, K, Ca, Mg, and Fe, increased significantlywith higher FAA. Alkalinity, conductivity, and water holding capacity of thesoil in experimental fields followed the similar trend; but total nitrogen,available phosphorus and organic carbon followed the opposite trend. Theamounts of heavy metals (Mn, Zn, Pb, Cr, Ni, Cd, and Cu), in both total andphyto-available forms significantly increased with higher FAA.                At lower levels of amendment, FAsignificantly induced the growth performance of both rice and mung bean plants.Grain /seed yield and quality of grains / seeds also responded similarly. At 10% FAA, yield increased by 17.7 to 41.4% in rice and 29.5 to 40.6% in mung beanplants, over that in the controls. Differential cultivar responses were alsoobserved among both the test plants. Cultivar Sugandha-3 and Malviya Jyoti,showed best performance amongst all the rice and mung bean cultivars, under FAtreatments. However, at higher doses, FA inhibited the growth and yieldtogether of both the test plants. The accumulation of all heavy metals, indifferent plant parts, grains and seeds, increased at all levels of FAA. It isconcluded that up to a certain level FAA could be beneficial for Indianagricultural fields and can be utilized as feasible management strategy for thedisposal of this major industrial waste.